Sulfonium salt compounds are substances that generate an acid when irradiated with an energy beam such as light, and they are used as, for example, photoacid generators in photolithography resist compositions used for the formation of electronic circuit such as a semiconductor, and cationic polymerization initiators contained in photopolymerizable compositions such as resin compositions for stereolithography, paints, coatings and adhesives.
With regard to sulfonium salt compounds, Patent Document 1 discloses a coumarin derivative; however, the coumarin derivative is disclosed as a hypoglycemic agent, and the Patent Document 1 merely describes that the coumarin derivative is useful for the treatment and prevention of diabetes and offers no description that the coumarin derivative may be used as a photoacid generator. In addition, Patent Document 2 discloses a cationic polymerization initiator which comprises a sulfonium salt having a coumarin skeleton, and Patent Document 3 discloses a heterocycle-containing sulfonium salt that is useful as, for example, a cationic photopolymerization initiator and an acid generator for chemically amplified resists. However, these Patent Documents suggest neither an alkoxy group nor an arylalkoxy group as a substituent of a coumarin skeleton, and do not indicate a structure which comprises sulfonium at the 3-position of a coumarin skeleton.